Analysis of gases



Noy. 23, 1943. A. P. SULLIVAN 2,335,032

ANALYSIS OF GASES Filed on. 12, 1940 INVEN TOR A LAN P-SOLLIVAN ATT R'NEY.

Patented Nov. 23,- 1943 7 UNITED STATES PATENT OFFICE ANALYSIS OF cases Alan P. Sullivan, Elizabeth, N. 1., assignor to Cities Service Oil Company, New York, N. Y., a. corporation oi.' Pennsylvania Application October 12, 1940, Serial No. 360,862

Claims.

best practice demands the use of air or oxygen in excess of that necessary to effect complete combustion of the fuel. However, the use of too great an excess of air or oxygen must be avoided, since this entails a loss of heat in the form of sensible heat taken up and removed from the combustion zone by the excess air. Correct adjustment of the proportions of air and fuel supplied to the combustion zone can best b made from information obtained by periodic or continuous analysis of the waste gases from the combustion operation to measure theamount of excess oxygen present.

Method of gas analysis are now known accordingto which hydrogen or other combustible is added to a gas under analysis for its oxygen content, after' which the gas mixture is passed through a combustion cell and combustion reaction between the oxygen and the combustible is promoted by contact with a heated catalyst. The temperature increase of the catalyst which results from the combustion can then be measured electrically, as by employing a Wheatstone bridge circuit whch incorporates the catalyst and a galvanometer. Most known methods for analyzing gas quantitatively for oxygen content have proved unsatisfactory and unreliable for continuous commercial use because of dimculties encountered in maintaining the calibration of an analyzing instrument by reason of deterioration of the catalyst and variations in rate of gas flow and in gas composition.

Another object of the present invention is to provide improved method and means adapted for making accurate quantitative gas analyses independently of variationsin rate of gas flow and independently of catalyst deterioration.

Another object of the present invention is to provide an instrument of. simpIerdesign hich can be readily operated and calibrated by an unskilled operator.

The improved gas analyzing instrument of the present invention employs duplicate combustion chambers through which balanced streams of gas to be tested and air or other comparison'gas are respectively forced by duplicate gas pumping units. Duplicate amounts of hydrogen or other combustible are added to both gas streams in amount suflicient to insure complete reaction of oxygen present in the air passing through the one combustion chamber. In passing through the combustion chambers the respective gas an air streams are likewise'contacted with duplicate catalyst wire filaments both preheated to a uniform temperature which is above the ignition temperature of any combustion components in the gas contacting the catalyst. Any differential temperature thereby developed at the'surfacesof the two catalysts by combustion is measured by a Wheatstone bridge electric circuit which inc'orporates both catalyst filaments as variable legs.

' Calibration of the instrument in simply effected by passing balanced streams of air admixed with equal volumes of hydrogen through both combustion chambers.

With the abpve and other objects and features in view, the invention will be hereinafter described by reference to the accompanying drawing, in which: I

Fig. l is a diagrammatic illustration of preferred apparatus arrangement in which certain parts are displayed in vertical section, while the pump unit is shown in perspective with one end removed; and Fig. 2 is a wiring diagram of a Wheatstone bridge circuit suitable for use with the apparatus of Fig. 1.

In the drawing, numerals H), l2 designate duplicate hollow tubular combustion cells each having gas inlet ports at their lower ends and gas exit ports at their upper ends. Duplicate imperforate cup-shaped baffles l4, I6 are disposed respectively in the central portion of each combustion cell in baffling relation to gas flowing therethrough. Multi-apertured screens l8 are.

shown as stretched across the open tops of each of the cups l4, l6 for the purpose of interfering with access of gas to the interior of the cups except by diffusion.

Secured within the cells l0, l2 respectively are corresponding ignition elements in the form of wire filaments 20, 22 of a heat refractory metal which is catalytic. Such wire filaments may be constructed of platinum or platinum alloy, or preferably of cerium oxide coated platinum. Other non-catalytic filaments orwires 24. 26 (preferably of gold plated platinum) mounted respectively in'cells I0, I2. As shown in Fig. 2, these catalyst and non-catalyst wire filaments are electrically connected as the .variaare also 'tially constant current supply.

ble and fixed resistance legs, respectively, of a Wheatstone bridge circuit which also include a millivoltmeter 28 and a source of heating current which has been illustrated as comprising an A. C.- D. C. transformer-rectifier assembly which incorporates an amperite 29 for insuring substan- A pair of compensating resistances 30, 32 are shown as mounted in series respectively with the catalyst wire filaments 28, 22 in the variable legs of the bridge.

A pump unit 34 is provided to develop flow of gas mixture to be analyzed through cell l and a corresponding flow of air through comparison cell l2. Pump unit 34 has a housing with an elliptical bore 35 within which is mounted a cylindrical rotor 36. The major longitudnal axis of rotor 36 coincides with that of bore 35, and the outside surface of rotor 36 is dimensioned to form a tight journal fit within the bore 35 along the minor axis of the ellipse. With rotor 36 so mounted, two non-communicating pum'p compartments 38 and 48 of equal displacement are formed in the bore on opposite sides of the rotor. Rotor slots are formed at uniformly spaced distances around the periphery of the rotor, and blades 42 are mounted to reciprocate in these slots; such blades having their outer ends always held in wiping contact with the walls of the bore by an elliptical shaped blade guide 44. Blade guide 44 is shown as centered withinthe bore and as shaped to conform thereto, with its major and minor axes coinciding with those of the bore.

For clearer illustration, the pump has been shown in perspective without its near end plate in place. Guide 44 would normally be attached to such end plate.

Two suction ports 46, 48 for the respective pump compartments 38 and 48 are located in the housing at the corresponding intake ends of the said compartments. The rotor of the pump is shown as rotating in a' clockwise direction with the suction ports located respectively at opposite ends of one diameter of' the rotor and at points equidistant from and adjacent to the minor axis of the elliptical bore. Discharge or exit ports 50 and 52 respectively open out of; the discharge ends of compartments 88 and 40 at points equidistant from the minor axis of the bore and equidistant from the suction ports. Rotor 38; is driven from an electric motor 54 by means of a shaft 56. Suction port 46 of pump chamber 88 is connected to a source 68 of gas to be analyzed by means of a conduit 60 which incorporates a filter 62 and a double throw valve 64. The discharge port 50 of pump chamber 38 is connected by a conduit n te the bottom intake port of cell l8. Where a continuous supp y of gas is available to be analyzed the supply is connected with the inlet 58. Provision, however, is made by which an isolated sample may be collected to be analyzed. To accomplish this a bellows pump 66(Figure 1) is connected with an inlet pipe 68 through a check valve 63. When the bellows is opened a sample of gas will be drawn in through the inlet 68 and stored in the bellows by the draw a sample from the bellows for making the analysis.

Suction port 48 of pump chamber 48 communicates with the outside atmosphere and is designed to function as man intake port. Discharge port 52 of chamber 48 is connected to the lower part of cell I 2 by a conduit 14. Conduits l2 and 14 should be of identical cross-section and are preferably each equipped with relief valves 16 for the purpose of insuring balanced pressures in the two conduits. Two identical hydrogen cells 18 are shown as connected respectively to conduits l2 and 14 by hydrogen supply pipes 88 and 82.

In the operation of the analyzer, the Wheatstone bridge is first balanced by passing uniform streams of air admixed with hydrogen through both cells I!) and I2. During this calibration, the source of gas 58 would be disconnected from the conduit 60 to allow air only to be drawn through this conduit into the pump chamber 38. The supplies of hydrogen from generators 18 are adjusted to deliver balanced streams of hydrogen to both cells in amount suflicient to insure complete combustion of the 21% of oxygen present in the air streams passing through both cells.

' After the calibration has been completed, conduit 68 is connectedwith the source 58 of gas to be analyzed, and a stream of gas to be analyzed is then passed through cell ID in admixture with the hydrogensupp'lied from one hydrogen cell, while continuing the. delivery of air admixed with hydrogen at a' uniform rate through cell l2 from pump chamber 40. The amount of oxygen in the gas under analysis will normally be less than the oxygen content of the air passing through cell l2, with the'result that the temperature of the catalyst wire 20 will be lower than the temperature of the catalyst wire 22. This will develop an unbalance of the Wheatstone bridge,and the amount of the unbalance, as measured by the millivoltmeter 28, will indicate the relative amount of oxygen in the gas sample passing through cell I 0 with respect to the known amount of oxygen in the air sample passing through cell l2.

Having thus described the invention in its preferred form, what is claimed asnew is:

1. In analyzing a mixture of gas quantitatively for oxygen content, the steps comprising passing a stream of the gas mixture at a uniform rate through one combustion cell and simultaneously passing a stream of air of known oxygen content at a corresponding rate through a second like check valve 63. At the same time the pressure to analyze this sample the double-throw valve 84 is rotated to connect the bellows pump with the inlet pipe 88 oi the pump 38. The pump will then combustion cell, adding a combustible gas in equal amount to the gas and air streams before they enter the respective combustion cells, the amount of combustible gas added being suilicient to insure complete combustion of the maximum oxygen content in either of the gas and air streams, contacting the gas and air streams in each cell with like combustion catalyst filaments while electrically heating said filaments to a temperature above the ignition temperature of the oxygen and combustible-gas constituents, and measuring any temperature differential developed between the catalyst filaments as a result of combustion of the respective oxygen constituants in the two streams.

2. Apparatus for analyzing gas quantitatively for its oxygen content comprising a pair of duplicate combustion cells, a Wheatstone bridge electric circuit having a pair of active catalyst legs and a pair of inactive legs, an active and an active leg of said bridge being mounted, in @2311 cell, duplicate pumping means with connections mounted for passing a stream of gas to be analyzed for its oxygen content at a uniform rate through one combustion cell and for simultaneously passing a stream of air of known oxygen content at a corresponding rate through the second combustion cell, means having conduits for introducing hydrogen at uniform rates into the connections for the gas and air streams entering the respective cells, and a millivoltmeter shunted across the bridge for measuring bridge unbalance in terms of oxygen content of the gas under analysis.

3. Apparatus as defined in claim 2 together with imperforate cup bafiles disposed within each combustion cell in the path of gas and air streams fiowing'therethrough, said cells having the catalyst filaments mounted within said'cups,

and apertured shielding elements mounted over the open end of each cup whereby to shield the catalyst wires against direct flow contact with the gas stream while permitting the constituents of the stream to contact the filaments by difiusion and convection.

4. The apparatus as defined in claim 2 in which a variable volume bellows-like pump of relatively large storage capacity has a, valved connection with the gas inlet of the duplicate pumping means for delivering gas to the pumping means,

aid bellows pump having a check valve inlet and a pressure relief valve.

5. A method of analyzing a gas to determine its oxygen content, the steps which comprise passing a stream of the gas to be analyzed at a uniform rate through a combustion cell, simultaneously passing a, stream of air at ,a corresponding rate through a combustion cell of substantially the same shape and arrangement as 10 the first-mentioned combustion cell, generating hydrogen in separate cells in substantially the same volume and adding hydrogen from one cell to the stream of air and from the other cell to the stream of gas to be tested, the amount of hy- 5 drogen being added in each case being sufllcient to completely burn any oxygen in the air or gas sample, contacting the gas and air streams in each cell with combustion catalysts of substantially the same properties and arrangement, said 20 combustion catalysts being heated in each cell to substantially the same temperature which is above the ignition temperature of the oxygen and hydrogen constituents in the streams passing through the cells, and measuring any temperag ture din'erential developed between the catalyst filaments as the result of combustion of-the oxygen contents of the gases in the respective streams.

ALAN P. SULLIVAN. 

